This proposal is a continuation of an existing grant with the overall objective of investigating the regulation of the levels of the messenger RNA's for cytochrome P450b and P450c. The appropriate mRNA was extracted from immunoprecipitated polysomes after oligo-dT cellulose chromatography. The synthesis of cDNA was catalyzed by reverse transcriptase and the cDNA was used to assess the levels of the respective mRNA in fetal, neonatal and adult livers; in rats that had been treated with either 3-methylcholanthrene or phenobarbital. A double-stranded cDNA was synthesized by DNA polymerase I, the hairpin hydrolyzed by Sl-nuclease and the cDNA was ligated to nuclease treated pBR322. After transformation of E. coli chi 1776 with the reconstructed plasmid, the bacteria were amplified, and large quantities of plasmid DNA were extracted after nuclease treatment, the cDNA was recovered, was nick-translated and used as a probe for the genome studies. The genomes for cytochrome P450b and P450c were screened for in a rat genomic library contained in Charon 4A lambda phage-infected E. coli. Appropriate clones were grown and restriction nuclease maps of these genomes were determined. Whether or not intervening sequences occurred in either of these genomes was also determined. Finally, some preliminary information about the relationship of each of these genomes to each other was sought.